Population Dynamics of the Gypsy Moth in Oak Forests in the Forest Steppes of European Russia

Abstract

There were five major outbreaks of the gypsy moth (Lymantria dispar L.) population between 1977 and 2018. The representation of the phases combined with the their ecological and population indices made it possible to recognize the eruptive and relatively prodromal cycles in the dynamics. The permanent outbreak was a feature of the coppice oak forests in southeastern Europe. The mean population size of the gypsy moth was higher, the maximum density and range of fluctuations were lower, the minimum density was significantly higher, and long periods of time between the outbreaks were not found under the optimum conditions in degraded forest stands with a simple structure growing in a dry climate. The outbreaks occurred every 10 years, while the population fluctuations could be characterized by cycles of various intensity. An eruptive stage was followed by a less intense outbreak (relatively prodromal stage), which differed from conventional prodromal stage by the recovery of the population at a level above stable, which immediately led to a fast growth and a new outbreak. The reason was the insufficient controls set by the complex of polytrophic entomophags, which held the population of gypsy moths at a low to near-average number.